Enzymes are proteins which catalyze a wide variety of chemical reactions, many of great commercial importance. Many enzymes are produced by culturing specific strains of molds, yeast or bacteria. The microbiological synthesis of enzymes is increasing in importance due to the fact the fermentation times are short, the growth media are inexpensive, and simple screening procedures of enzymatic activity have been developed. Typically, an enzyme-producing microorganism is grown under controlled conditions in an aqueous medium containing nutrients, buffers and the like. The growth of the microorganism may be terminated, which "stops" the production of enzyme, and the enzyme is then stabilized, for example, by the addition of chemicals such as polyethylene glycols. However, even in the presence of stabilizers, enzymatic activity often decreases in aqueous media. Therefore, such enzyme-containing solutions must either be shipped and used soon after receipt, or the enzymes must be isolated in the dry state.
Dry enzyme concentrates are desirable for a number of reasons: (a) their activity remains substantially constant for an indefinite period of time under ambient conditions; (b) due to their high activity per unit weight, they are much more economical to store and ship than are aqueous solutions; and (c) they can be readily redissolved to form solutions of varying, precisely-controlled activities.
The advantages of dry enzyme preparations have encouraged the development of methods to remove the large excesses of water from the relatively minor amounts of active solids which are dissolved or suspended therein. However, all of the currently available methods suffer from a number of significant disadvantages. Lyophilization preserves enzymatic activity but is extremely energy intensive due to the need to maintain high vacuums for long periods of time. Chemical precipitation requires expensive additives and often requires further purification steps to remove them after the residue has been isolated. Effective spray-drying requires either tower temperatures which lead to unacceptable enzyme deactivation or expensive enzyme recycling mechanisms.
Therefore, methods are needed for drying aqueous solutions of enzymes which allow substantial enzymatic activity to be retained in the dried products. A useful method should produce dry enzyme concentrates rapidly and employ moderate processing conditions.